“Lazy” Sunday

18102009

First off, still no pictures. I didn’t fix my camera and didn’t think to ask anyone else for theirs. You’ll see why when you read on.

Chris and I ended up spending our energy on this “lazy” Sunday on a bit of a wild goose chase. Last week when Chris tested out the IMU (the inertial navigation unit which is basically a set of very fancy gyroscopes that tell ENDURANCE in what direction it’s pointing and is one of the most important navigation instruments on the robot), it was not giving any data. The IMU needs to go through an initialization before every mission. This initialization requires telling it what it’s approximate latitude and longitude are. Chris had entered coordinates he’d gotten from Google Earth for this, but wasn’t exactly sure of the format for the numbers and wanted me to double check.

I thought we could get this quickly done today after brunch, so we came down to the incinerator. I glanced at the configuration file Chris had modified with the new coordinates, and it all looked good to me, so we tried running the IMU again. Didn’t work. The IMU would say it was initializing, but then never switch over to sending data.

After an afternoon of back and forth testing and thinking about what could be causing this problem, including mobilizing Rachel and Vickie to come down and start taking the IMU case out of the middle of the robot (Vickie politely suggested we try a few more things on the software side before initializing a multi-hour disassembly and reassembly process) and contacting the manufacturer (who immediately started a help ticket for us), we finally figured out just a little while ago that the problem was, in fact… the format of the numbers for latitude and longitude. Chris had entered degrees and decimal degrees instead of degrees and decimal minutes. Though these numbers didn’t make any sense, our code on the ENDURANCE central processor which then sends this information to the IMU didn’t complain about this at all, and disregarded any complaint from IMU itself. I certainly hadn’t picked up on the fact that the latitude should be -77 49.8666 instead of -77 83.3111, both looked pretty reasonable to me. So we were left running around thinking one of the most important, most expensive instruments on the robot was broken, when we were actually telling it nonsense and couldn’t understand it was just saying “Huh?”

I have to say, this situation wasn’t totally unfamiliar. I’ve generally found that there’s something about how we’re wired that naturally leads to going way down the wrong path in figuring something out, when the actual answer is something quite simple, usually the first thing you thought of but then never really took the time to thoroughly and conscientiously investigate. Luckily, today we had Vickie to remind us to go back and check things a little more before hurtling down an even longer path towards no result.

I’d be in favor of us all using radians or, even better, fractions of arc (radians/2pi). Mixing sexagesimal and decimal numbers is always confusing and cumbersome, and the decimal minutes used by the IMU are about as mixed up as you can get. If you’re already going to use degrees, might as well go all the way and use minutes and seconds.